为了研究挤奶机系统真空度不同时的挤奶效果,解决目前挤奶机使用中系统真空度缺乏科学设定依据的问题,该文以12头高产泌乳牛(单产(7.4±0.4)t)为试验对象,以体细胞数(somatic cell count,SCC)、乳头末端壁厚变化率以及挤奶量等作为挤奶效果评价指标参数,在系统真空度分别为44、46以及48 kPa时,研究了系统真空度对泌乳牛挤奶过程不同阶段的内套真空度和挤奶杯口真空度的影响,量化了系统真空度对挤奶效果评价指标的影响程度.研究表明,当系统真空度从44 kPa增加至48 kPa时,挤奶量、挤奶时间以及平均奶流量均无显著差异,但体细胞数的对数(P<0.05)和乳头末端壁厚变化率(P<0.05)均显著增加.研究认为试验挤奶机用44 kPa的系统真空度比用46或48 kPa时的效果更好.该文为中国挤奶机使用中系统真空度的优化设置提供技术支持.%The same type of milking machine has the different system vacuum degree, and its set value is mainly from experience and lacks a specific scientific basis. However, during milk processing, farms keep the factory setting value of system vacuum degree for all dairy cows, which causes obvious health problems of dairy cows. Therefore, it is imperative to provide the scientific setting basis of system vacuum degree by quantifying the effect of milking machine system vacuum degree on milking characteristics and cows' health. The dry test and wet test were carried out at China Agricultural Machinery Testing Centre. Simulation milking device was applied to simulate peak milking process with the milk flow of 4.0 kg/min for the high yield dairy cow and 2.5 kg/min for the low yield dairy cow. The pulsation rate and pulsation ratio were set to 60 cycles/min and 60%, respectively, which remained unchanged throughout the experiment. System vacuum degree was set at 44, 46 and 48 kPa, respectively, by means of the vacuum regulator. VaDia vacuum tester was used for data acquisition when milking machine ran under no-load or simulated the milking process at each system vacuum degree. The milking time test was carried out at a dairy cattle field in the north of Jinan, Shandong Province. The setting program of pulsation rate and pulsation ratio was the same in dry test and wet test. Twelve high yielding Chinese Holstein cows were randomly selected. In continuous 3 months (from July to September), milking machine system vacuum degree was set at 44, 46 and 48 kPa respectively. Milking was performed at 5:00 and 17:00 every day, and milk yield, somatic cell count (SCC), milking time (only in morning milking) and teat end wall thickness before and after milking (only in morning milking) were measured. All parameters measured were compared with ANOVA (analysis of variance) using SPSS. The comparisons of multiple means were made using the Duncan's multiple range test, in order to classify the effect of the different treatments. The logarithm of SCC was used to normalize the distribution of SCC. The results showed that during peak milk flow period and over milking period, system vacuum degree was increased from 44 to 48 kPa, and the increasing rate of liner vacuum degree was 4.9% (P<0.001) and 10.8% (P<0.001), respectively. Meanwhile, the increasing rate of milking cup mouth vacuum degree was 373.8% (P<0.001) and 53.7%(P<0.001), respectively. There were no significant differences for milk yield, average milk flow rate and milking time except the logarithm of SCC (P<0.05) between 44 and 48 kPa system vacuum degree. Percentage change of the teat end wall thickness was lower at the lower system vacuum level (44 kPa) after milking, and increased (P<0.05) as the system vacuum level was raised to 48 kPa. The findings of this study indicated that with a lower vacuum level of 44 kPa, the cows were milked better than those with 46 or 48 kPa. The findings in current work provide a technical support for the optimization settings of working state parameters of milking machine in mechanization milking parlors in China.
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